He didn't just want a bike for Christmas - Sai Hope Daunibau wanted a new hand to ride it with.

Yesterday, thanks to a limb specialist who was in on the secret Santa surprise, he got his wish.

The 8-year-old Wellingtonian lost part of his left arm after being hit by a bus in Fiji while on a family holiday in August, and two months later was given a prosthetic limb.

But the hand did not allow him to grip the handlebars of a bike - until Otto Schutte from the Wellington Limb Centre made him a new one.

Yesterday, even as Sai was fitted with a new "gripping" hand, he had no idea what it was for - until his family took him straight from the clinic to a bicycle shop.

Schutte, a senior clinical prosthetist, ordered the parts from the same German company that makes limbs for Paralympians.

The gripping hand was specially designed to enable Sai to ride a bicycle.

"One of the rewarding moments for me is to see an arm that I've made come back to me a wreck, because that means they've been properly using it."

Schutte has been working with Sai since the Newtown School boy was flown back to New Zealand from Fiji for urgent surgical treatment, with the help of donations raised by the Wellington Rugby Football Union junior codes.

He fitted Sai's first prosthesis two months ago, and explained how he designed a "sock" to fit his patient's stump and then was tasked with matching the length of the arm and skin colour.

An occupational therapist taught Sai how to flex and clench his new arm and hand using a switch and shoulder movements, which he proudly demonstrated yesterday.

Sai had thrown himself back into his daily routine with energy since the accident, Mum Vulori Daunibau said.

"He's been going out of his way to get back into sports. We were encouraging him to try soccer, but he's still keen on rugby."

The family found a suitable bike for Sai yesterday after some trial and error, because he needed one with rear-wheel brakes that operated from the right-hand side.

Sai was brief in his appraisal of his two new Christmas presents - the hand was "great," he said, and as for whether life had changed much since the accident: "The same."